Note: Descriptions are shown in the official language in which they were submitted.
CA 02857857 2014-07-25
HIGH OCTANE UNLEADED AVIATION GASOLINE
Field of the Invention
The present invention relates to high octane unleaded aviation gasoline fuel,
more
particularly to a high octane unleaded aviation gasoline having low-oxygen
content.
Background of the Invention
Avgas (aviation gasoline), is an aviation fuel used in spark-ignited internal-
combustion engines to propel aircraft. Avgas is distinguished from mogas
(motor
gasoline), which is the everyday gasoline used in cars and some non-commercial
light
aircraft. Unlike mogas, which has been formulated since the 1970s to allow the
use of 3-
way catalytic converters for pollution reduction, avgas contains tetraethyl
lead (TEL), a
non-biodegradable toxic substance used to prevent engine knocking
(detonation).
Aviation gasoline fuels currently contain the additive tetraethyl lead (TEL),
in
amounts up to 0.53 mL/L or 0.56 g/L which is the limit allowed by the most
widely used
aviation gasoline specification 100 Low Lead (100LL). The lead is required to
meet the
high octane demands of aviation piston engines: the lOOLL specification ASTM
D910
demands a minimum motor octane number (MON) of 99.6, in contrast to the EN 228
specification for European motor gasoline which stipulates a minimum MON of 85
or
United States motor gasoline which require unleaded fuel minimum octane rating
(R+M)/2
of 87.
Aviation fuel is a product which has been developed with care and subjected to
strict regulations for aeronautical application. Thus aviation fuels must
satisfy precise
physico-chemical characteristics, defined by international specifications such
as ASTM
D910 specified by Federal Aviation Administration (FAA). Automotive gasoline
is not a
fully viable replacement for avgas in many aircraft, because many high-
performance
and/or turbocharged airplane engines require 100 octane fuel (MON of 99.6) and
modifications are necessary in order to use lower-octane fuel. Automotive
gasoline can
vaporize in fuel lines causing a vapor lock (a bubble in the line) or fuel
pump cavitation,
starving the engine of fuel. Vapor lock typically occurs in fuel systems where
a
mechanically-driven fuel pump mounted on the engine draws fuel from a tank
mounted
lower than the pump. The reduced pressure in the line can cause the more
volatile
components in automotive gasoline to flash into vapor, forming bubbles in the
fuel line and
interrupting fuel flow.
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The ASTM D910 specification does not include all gasoline satisfactory for
reciprocating aviation engines, but rather, defines the following specific
types of aviation
gasoline for civil use: Grade 80; Grade 91; Grade 100; and Grade 1 OOLL. Grade
100 and
Grade lOOLL are considered High Octane Aviation Gasoline to meet the
requirement of
modern demanding aviation engines. In addition to MON, the D910 specification
for
Avgas have the following requirements: density; distillation (initial and
final boiling
points, fuel evaporated, evaporated temperatures T10, T40, T90, TIO T50);
recovery, residue,
and loss volume; vapor pressure; freezing point; sulfur content; net heat of
combustion;
copper strip corrosion; oxidation stability (potential gum and lead
precipitate); volume
change during water reaction; and electrical conductivity. Avgas fuel is
typically tested for
its properties using ASTM tests:
Motor Octane Number: ASTM D2700
Aviation Lean Rating: ASTM D2700
Performance Number (Super-Charge): ASTM D909
Tetraethyl Lead Content: ASTM D5059 or ASTM D3341
Color: ASTM D2392
Density: ASTM D4052 or ASTM D1298
Distillation: ASTM D86
Vapor Pressure: ASTM D5191 or ASTM D323 or ASTM D5190
Freezing Point: ASTM D2386
Sulfur: ASTM D2622 or ASTM D1266
Net Heat of Combustion (NHC): ASTM D3338 or ASTM D4529 or ASTM
D4809
Copper Corrosion: ASTM D130
Oxidation Stability - Potential Gum: ASTM D873
Oxidation Stability - Lead Precipitate: ASTM D873
Water Reaction - Volume change: ASTM D1094
Electrical Conductivity: ASTM D2624
Aviation fuels must have a low vapour pressure in order to avoid problems of
vaporization (vapor lock) at low pressures encountered at altitude and for
obvious safety
reasons. But the vapor pressure must be high enough to ensure that the engine
starts easily.
The Reid Vapor pressure (RVP) should be in the range of 38kPa to 49kPA. The
final
distillation point must be fairly low in order to limit the formations of
deposits and their
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CA 02857857 2014-07-25
harmful consequences (power losses, impaired cooling). These fuels must also
possess a
sufficient Net Heat of Combustion (NHC) to ensure adequate range of the
aircraft.
Moreover, as aviation fuels are used in engines providing good performance and
frequently
operating with a high load, i.e. under conditions close to knocking, this type
of fuel is
expected to have a very good resistance to spontaneous combustion.
Moreover, for aviation fuel two characteristics are determined which are
comparable to octane numbers: one, the MON or motor octane number, relating to
operating with a slightly lean mixture (cruising power), the other, the Octane
rating.
Performance Number or PN, relating to use with a distinctly richer mixture
(take-off).
With the objective of guaranteeing high octane requirements, at the aviation
fuel
production stage, an organic lead compound, and more particularly
tetraethyllead (TEL), is
generally added. Without the TEL added, the MON is typically around 91. As
noted
above ASTM D910, 100 octane aviation fuel requires a minimum motor octane
number
(MON) of 99.6. The distillation profile of the high octane unleaded aviation
fuel
composition should have a T10 of maximum 75 C, T40 of minimum 75 C, T50
maximum
105 C, and T90 of maximum 135 C.
As in the case of fuels for land vehicles, administrations are tending to
lower the
lead content, or even to ban this additive, due to it being harmful to health
and the
environment. Thus, the elimination of lead from the aviation fuel composition
is becoming
an objective.
Summary of the Invention
It has been found that it is difficult to produce a high octane unleaded
aviation fuel
that meet most of the ASTM D910 specification for high octane aviation fuel.
In addition
to the MON of 99.6, it is also important to not negatively impact the flight
range of the
aircraft, vapor pressure, temperature profile and freeze points that meets the
aircraft engine
start up requirements and continuous operation at high altitude.
In accordance with certain of its aspects, in one embodiment of the present
invention provides a an unleaded aviation fuel composition having a MON of at
least 99.6,
sulfur content of less than 0.05wt%, CI-IN content of at least 97.2wt%, less
than 2.8 wt% of
oxygen content, a T10 of at most 75 C, T40 of at least 75 C, a T50 of at most
105 C, a
T90 of at most 135 C, a final boiling point of less than 190 C, an adjusted
heat of
combustion of at least 43.5 MJ/kg, a vapor pressure in the range of 38 to 49
kPa,
comprising a blend comprising:
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from 20 vol.% to 35 vol.% of toluene having a MON of at least 107;
from 2 vol.% 10 vol.% of aniline;
from above 30vol% to 55 vol% of at least one alkylate or alkyate blend having
an
initial boiling range of from 32 C to 60 C and a final boiling range of from
105 C
to 140 C, having T40 of less than 99 C, T50 of less than 100 C, T90 of less
than
110 C, the alkylate or alkylate blend comprising isoparaffins from 4 to 9
carbon
atoms, 3-20vol% of C5 isoparaffins, 3-15vol% of C7 isoparaffins, and 60-90
vol%
of C8 isoparaffins, based on the alkylate or alkylate blend, and less than 1
vol% of
C10+, based on the alkylate or alkylate blend;
from 7 vol% to 14 vol% of a branched alkyl acetate having branched chain alkyl
group having 4 to 8 carbon atoms; and
at least 8 vol% of isopentane in an amount sufficient to reach a vapor
pressure in
the range of 38 to 49 kPa; and
wherein the fuel composition contains less than 1 vol% of C8 aromatics.
The features and advantages of the invention will be apparent to those skilled
in the
art. Numerous changes may be made by those skilled in the art. The scope of
the claims
should not be limited by the preferred embodiments set forth in the examples,
but should
be given the broadest interpretation consistent with the description as a
whole.
Brief Description of the Drawings
This drawing illustrates certain aspects of some of the embodiments of the
invention, and should not be used to limit or define the invention.
Fig. 1 shows the engine conditions for unleaded aviation fuel Example 1 at
2575
RPM at constant manifold pressure.
Fig. 2 shows the detonation data for unleaded aviation fuel Example 1 at 2575
RPM
at constant manifold pressure.
Fig. 3 shows the engine conditions for unleaded aviation fuel Example 1 at
2400
RPM at constant manifold pressure.
Fig. 4 shows the detonation data for unleaded aviation fuel Example 1 at 2400
RPM
at constant manifold pressure.
Fig. 5 shows the engine conditions for unleaded aviation fuel Example 1 at
2200
RPM at constant manifold pressure.
Fig. 6 shows the detonation data for unleaded aviation fuel Example 1 at 2200
RPM
at constant manifold pressure.
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Fig. 7 shows the engine conditions for unleaded aviation fuel Example 1 at
2757
RPM at constant power.
Fig. 8 shows the detonation data for unleaded aviation fuel Example 1 at 2757
RPM
at constant power.
Fig. 9 shows the engine conditions for FBO sourced 1 OOLL fuel at 2575 RPM at
constant manifold pressure.
Fig. 10 shows the detonation data for FBO sourced 1 OOLL fuel at 2575 RPM at
constant manifold pressure.
Fig. 11 shows the engine conditions for FBO sourced 1 OOLL fuel at 2400 RPM at
constant manifold pressure.
Fig. 12 shows the detonation data for FBO sourced 1 OOLL fuel at 2400 RPM at
constant manifold pressure.
Fig. 13 shows the engine conditions for FBO sourced lOOLL fuel at 2200 RPM at
constant manifold pressure.
Fig. 14 shows the detonation data for FBO sourced 1 OOLL fuel at 2200 RPM at
constant manifold pressure.
Fig. 15 shows the engine conditions for FBO sourced 1 OOLL fuel at 2757 RPM at
constant power.
Fig. 16 shows the detonation data for FBO sourced lOOLL fuel at 2757 RPM at
constant power.
Detailed Description of the Invention
We have found that a high octane low oxygen-content unleaded aviation fuel
having an oxygen content of less than 2.8wt% based on the unleaded aviation
fuel blend
that meets most of the ASTM D910 specification for 100 octane aviation fuel
can be
produced by a blend comprising from about 20 vol.% to about 35 vol% of high
MON
toluene, from about 2 vol% to about 10 vol% of aniline; from about above 30
vol% to
about 55 vol% of at least one alkylate cut or alkylate blend that have certain
composition
and properties and at least 8vol% of isopentane and from about 7vol% to about
14vol% of
a branched alkyl acetate having branched chain alkyl group having 4 to 8
carbon atoms.
Preferably, the combined amount of toluene and the branched alkyl acetate in
the fuel
composition is more than 30vol%, more than 31 vol%, more than 32 vol%, or more
than
33vo1%. The high octane unleaded aviation fuel of the invention has a MON of
greater
than 99.6.
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In one embodiment, an unleaded aviation fuel composition having a MON of at
least 99.6, sulfur content of less than 0.05wt%, CHN content of at least
97.2wt%, less than
2.8 wt% of oxygen content, a T10 of at most 75 C, T40 of at least 75 C, a T50
of at most
105 C, a T90 of at most 135 C, a final boiling point of less than 190 C, an
adjusted heat
of combustion of at least 43.5 MJ/kg, a vapor pressure in the range of 38 to
49 kPa,
comprising a blend comprising:
from about 20 vol.% to about 35 vol.% of toluene having a MON of at least 107;
from about 2 vol.% to about 10 vol.% of aniline;
from above 30vol% to about 55 vol% of at least one alkylate or alkyate blend
having an initial boiling range of from about 32 C to about 60 C and a final
boiling
range of from about 105 C to about 140 C, having T40 of less than 99 C , T50
of
less than 100 C, T90 of less than 110 C, the alkylate or alkylate blend
comprising
isoparaffins from 4 to 9 carbon atoms, about 3-20vol% of C5 isoparaffins,
about 3-
15vol% of C7 isoparaffins, and about 60-90 vol% of C8 isoparaffins, based on
the
alkylate or alkylate blend, and less than lvol% of C10+, based on the alkylate
or
alkylate blend;
from about 7 vol% to about 14 vol% of a branched alkyl acetate having branched
chain alkyl group having 4 to 8 carbon atoms; and
at least 8 vol% of isopentane in an amount sufficient to reach a vapor
pressure in
the range of 38 to 49 kPa;
wherein the combined amount of toluene and the branched alkyl acetate in the
fuel
composition is more than 30vol%, preferably more than 33vo1%; and
wherein the fuel composition contains less than 1 vol% of C8 aromatics.
Further, the unleaded aviation fuel composition contains less than 1 vol% of
C8
aromatics. It has been found that C8 aromatics such as xylene may have
materials
compatibility issues, particularly in older aircraft. Further, it has been
found that unleaded
aviation fuel containing C8 aromatics tend to have difficulties meeting the
temperature
profile of D910 specification. In one embodiment, the unleaded aviation fuel
contains less
than 0.2vol% of ethers. In another embodiment, the unleaded aviation fuel
contains no
straight chain alcohols and no noncyclic ethers. In one embodiment, the
unleaded aviation
fuel contains no alcohols having boiling point of less than 80 C. Further, the
unleaded
aviation fuel composition have a benzene content between 0%v and 5%v,
preferably less
than 1%v.
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Further, in some embodiments, the volume change of the unleaded aviation fuel
tested for water reaction is within +/- 2mL as defined in ASTM D1094.
The high octane unleaded fuel will not contain lead and preferably not contain
any
other metallic octane boosting lead equivalents. The term "unleaded" is
understood to
contain less than 0.01g/L of lead. The high octane unleaded aviation fuel will
have a sulfur
content of less than 0.05 wt%. In some embodiments, it is preferred to have
ash content of
less than 0.0132g/L (0.05 g/gallon) (ASTM D-482).
According to current ASTM D910 specification, the NHC should be close to or
above 43.5mJ/kg. The Net Heat of Combustion value is based on a current low
density
aviation fuel and does not accurately measure the flight range for higher
density aviation
fuel. It has been found that for unleaded aviation gasoline that exhibit high
densities, the
heat of combustion may be adjusted for the higher density of the fuel to more
accurately
predict the flight range of an aircraft.
There are currently three approved ASTM test methods for the determination of
the
heat of combustion within the ASTM D910 specification. Only the ASTM D4809
method
results in an actual determination of this value through combusting the fuel.
The other
methods (ASTM D4529 and ASTM D3338) are calculations using values from other
physical properties. These methods have all been deemed equivalent within the
ASTM
D910 specification.
Currently the Net Heat of Combustion for Aviation Fuels (or Specific Energy)
is
expressed gravimetrically as MJ/kg. Current lead containing aviation gasoline
has a
relatively low density compared to many alternative unleaded formulations.
Fuels of
higher density have a lower gravimetric energy content but a higher volumetric
energy
content (MJ/L).
The higher volumetric energy content allows greater energy to be stored in a
fixed
volume. Space can be limited in general aviation aircraft and those that have
limited fuel
tank capacity, or prefer to fly with full tanks, can therefore achieve greater
flight
range. However, the more dense the fuel, then the greater the increase in
weight of fuel
carried. This could result in a potential offset of the non-fuel payload of
the
aircraft. Whilst the relationship of these variables is complex, the
formulations in this
embodiment have been designed to best meet the requirements of aviation
gasoline. Since
in part density effects aircraft range, it has been found that a more accurate
aircraft range,
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normally gauged using Heat of Combustion, can be predicted by adjusting for
the density
of the avgas using the following equation:
HOC* = (HOCadensity) (% range increase% payload increase +1)
where HOC* is the adjusted Heat of Combustion (MJ/kg), HOC, is the volumetric
energy density (MJ/L) obtained from actual Heat of Combustion measurement,
density is
the fuel density (g/L), % range increase is the percentage increase in
aircraft range
compared to 100 LL(HOCLL) calculated using HOC, and HOCLL for a fixed fuel
volume,
and % payload increase is the corresponding percentage increase in payload
capacity due
to the mass of the fuel.
The adjusted heat of combustion will be at least 43.5MJ/kg, and have a vapor
pressure in the range of 38 to 49 kPa. The high octane unleaded fuel
composition will
further have a freezing point of -58 C or less. Further, the final boiling
point of the high
octane unleaded fuel composition should be less than 190 C, preferably at most
180 C
measured with greater than 98.5% recovery as measured using ASTM D-86. If the
recovery level is low, the final boiling point may not be effectively measured
for the
composition (i.e., higher boiling residual still remaining rather than being
measured). The
high octane unleaded aviation fuel composition of the invention have a Carbon,
Hydrogen,
and Nitrogen content (CHN content) of at least 97.2wt%, preferably at least
97.5wt%,
and less than 2.8 wt%, preferably 2.5wt% of oxygen. Suitably, the unleaded
aviation fuel
have an aromatics content measured according to ASTM D5134 of greater than
15wt% to
about 35wt%.
It has been found that the high octane low oxygen-content unleaded aviation
fuel of
the invention not only meets the MON value for 100 octane aviation fuel, but
also meets
the freeze point and the temperature profile of T10 of at most 75 C, T40 of at
least 75 C,
150 at most 105 C, and T90 of at most 135 C, vapor pressure, adjusted heat of
combustion, and freezing point. In addition to MON it is important to meet the
vapor
pressure, temperature profile, and minimum adjusted heat of combustion for
aircraft engine
start up and smooth operation of the plane at higher altitude. Preferably the
potential gum
value is less than 6mg/100mL.
It is difficult to meet the demanding specification for unleaded high octane
aviation
fuel. For example, US Patent Application Publication 2008/0244963, discloses a
lead-free
aviation fuel with a MON greater than 100, with major components of the fuel
made from
avgas and a minor component of at least two compounds from the group of esters
of at
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least one mono- or poly-carboxylic acid and at least one mono-or polyol,
anhydrides of at
least one mono- or poly carboxylic acid. These oxygenates have a combined
level of at
least 15%v/v, typical examples of 30%v/v, to meet the MON value. However,
these fuels
do not meet many of the other specifications such as heat of combustion
(measured or
adjusted) at the same time, including even MON in many examples. Another
example, US
Patent No. 8313540 discloses a biogenic turbine fuel comprising mesitylene and
at least
one alkane with a MON greater than 100. However, these fuels also do not meet
many of
the other specifications such as heat of combustion (measured or adjusted),
temperature
profile, and vapor pressure at the same time.
Toluene
Toluene occurs naturally at low levels in crude oil and is usually produced in
the
processes of making gasoline via a catalytic reformer, in an ethylene cracker
or making
coke from coal. Final separation, either via distillation or solvent
extraction, takes place in
one of the many available processes for extraction of the BTX aromatics
(benzene, toluene
and xylene isomers). The toluene used in the invention must be a grade of
toluene that have
a MON of at least 107 and containing less than 1 vol% of C8 aromatics.
Further, the
toluene component must have a benzene content between 0%v and 5%v, preferably
less
than 1%v.
For example an aviation reformate is generally a hydrocarbon cut containing at
least 70% by weight, ideally at least 85% by weight of toluene, and it also
contains C8
aromatics (15 to 50% by weight ethylbenzene, xylenes) and C9 aromatics (5 to
25% by
weight propyl benzene, methyl benzenes and trimethylbenzenes). Such reformate
has a
typical MON value in the range of 102 - 106, and it has been found not
suitable for use in
the present invention.
Toluene is preferably present in the blend in an amount from about 20vol%,
preferably from about 25vo1%, to at most about 40vol%, preferably to at most
about
35vo1%, more preferably to at most about 30vol%, based on the unleaded
aviation fuel
composition.
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Aniline
Aniline (C6H5NH2) is mainly produced in industry in two steps from benzene.
First, benzene is nitrated using a concentrated mixture of nitric acid and
sulfuric acid at 50
to 60 C, which gives nitrobenzene. In the second step, the nitrobenzene is
hydrogenated,
typically at 200-300 C in presence of various metal catalysts.
As an alternative, aniline is also prepared from phenol and ammonia, the
phenol
being derived from the cumene process.
In commerce, three brands of aniline are distinguished: aniline oil for blue,
which is
pure aniline; aniline oil for red, a mixture of equimolecular quantities of
aniline and ortho-
and para-toluidines; and aniline oil for safranine, which contains aniline and
ortho-
toluidine, and is obtained from the distillate (echappes) of the fuchsine
fusion. Pure aniline,
otherwise known as aniline oil for blue is desired for high octane unleaded
avgas. Aniline
is preferably present in the blend in an amount from about 2%v, preferably at
least about
3%v, most preferably at least about 4%v to at most about 10%v, preferably to
at most
about 7%, more preferably to at most about 6%, based on the unleaded aviation
fuel
composition.
Alkylate and Alkyate Blend
The term alkylate typically refers to branched-chain paraffin. The branched-
chain
paraffin typically is derived from the reaction of isoparaffin with olefin.
Various grades of
branched chain isoparaffins and mixtures are available. The grade is
identified by the
range of the number of carbon atoms per molecule, the average molecular weight
of the
molecules, and the boiling point range of the alkylate. It has been found that
a certain cut
of alkylate stream and its blend with isoparaffins such as isooctane is
desirable to obtain or
provide the high octane unleaded aviation fuel of the invention. These
alkylate or alkylate
blend can be obtained by distilling or taking a cut of standard alkylates
available in the
industry. It is optionally blended with isooctane. The alkylate or alkyate
blend have an
initial boiling range of from about 32 C to about 60 C and a final boiling
range of from
about 105 C to about 140 C , preferably to about 135 C, more preferably to
about130 C,
most preferably to about 125 C, having T40 of less than 99 C, preferably at
most 98 C,
T50 of less than 100 C, T90 of less than 110 C, preferably at most 108 C, the
alkylate or
alkylate blend comprising isoparaffins from 4 to 9 carbon atoms, about 3-
20vol% of C5
isoparaffins, based on the alkylate or alkylate blend, about 3-15vol% of C7
isoparaffins,
based on the alkylate or alkylate blend, and about 60-90 vol% of C8
isoparaffins, based on
CA 02857857 2014-07-25
the alkylate or alkylate blend, and less than 1 vol% of C10+, preferably less
than 0.1vol%,
based on the alkylate or alkylate blend. Alkylate or alkylate blend is
preferably present in
the blend in an amount from about above 30%v, preferably at least about 32%v,
most
preferably at least about 35%v to at most about 55%v, preferably to at most
about 49%v,
more preferably to at most about 47%v based on the unleaded aviation fuel
composition.
Isopentane
Isopentane is present in an amount of at least 8 vol% in an amount sufficient
to
reach a vapor pressure in the range of 38 to 49 kPa. The alkylate or alkylate
blend also
contains C5 isoparaffins so this amount will typically vary between 5 vol% and
25 vol%
depending on the C5 content of the alkylate or alkylate blend. Isopentane
should be
present in an amount to reach a vapor pressure in the range of 38 to 49 kPa to
meet aviation
standard. The total isopentane content in the blend is typically in the range
of 10% to 26
vol%, preferably in the range of 12% to 18% by volume, based on the unleaded
aviation
fuel composition.
Co-solvent
The unleaded aviation fuel may contain a branched alkyl acetate having
branched
chain alkyl group having 4 to 8 carbon atoms as a co-solvent. Suitable co-
solvent may be,
for example, t-butyl acetate, iso-butyl acetate, ethylhexylacetate, iso-amyl
acetate, and t-
butyl amyl acetate, or mixtures thereof. The unleaded aviation fuels
containing aromatic
amines tend to be significantly more polar in nature than traditional aviation
gasoline base
fuels. As a result, they have poor solubility in the fuels at low
temperatures, which can
dramatically increase the freeze points of the fuels. Consider for example an
aviation
gasoline base fuel comprising 10% v/v isopentane, 70% v/v light alkylate and
20% v/v
toluene. This blend has a MON of around 90 to 93 and a freeze point (ASTM
D2386) of
less than ¨76 C. The addition of 6% w/w (approximately 4% v/v) of the aromatic
amine
aniline increases the MON to 96.4. At the same time, however, the freeze point
of the
resultant blend (again measured by ASTM D2386) increases to ¨12.4 C. The
current
standard specification for aviation gasoline, as defined in ASTM D910,
stipulates a
maximum freeze point of ¨58 C. Therefore, simply replacing TEL with a
relatively large
amount of an alternative aromatic octane booster would not be a viable
solution for an
unleaded aviation gasoline fuel. It has been found that branched chain alkyl
acetates
having an alkyl group of 4 to 8 carbon atoms dramatically decrease the
freezing point of
the unleaded aviation fuel to meet the current ASTM D910 standard for aviation
fuel. The
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branched acetate is present in an amount from about 7 vol%, preferably from
about 8 vol%,
to about 14 vol%, preferably to about 10vol%, based on the unleaded aviation
fuel
composition.
Blending
For the preparation of the high octane unleaded aviation gasoline, the
blending can
be in any order as long as they are mixed sufficiently. It is preferable to
blend the polar
components into the toluene, then the non-polar components to complete the
blend. For
example the aromatic amine and co-solvent are blended into toluene, followed
by
isopentane and alkylate component (alkylate or alkylate blend).
In order to satisfy other requirements, the unleaded aviation fuel according
to the
invention may contain one or more additives which a person skilled in the art
may choose
to add from standard additives used in aviation fuel. There should be
mentioned, but in
non-limiting manner, additives such as antioxidants, anti-icing agents,
antistatic additives,
corrosion inhibitors, dyes and their mixtures.
According to another embodiment of the present invention a method for
operating
an aircraft engine, and/or an aircraft which is driven by such an engine is
provided, which
method involves introducing into a combustion region of the engine and the
high octane
unleaded aviation gasoline fuel formulation described herein. The aircraft
engine is
suitably a spark ignition piston-driven engine. A piston-driven aircraft
engine may for
example be of the inline, rotary, V-type, radial or horizontally-opposed type.
While the invention is susceptible to various modifications and alternative
forms,
specific embodiments thereof are shown by way of examples herein described in
detail. It
should be understood, that the detailed description thereto are not intended
to limit the
invention to the particular form disclosed, but on the contrary, the intention
is to cover all
modifications, equivalents and alternatives falling within the spirit and
scope of the present
invention as defined by the appended claims. The present invention will be
illustrated by
the following illustrative embodiment, which is provided for illustration only
and is not to
be construed as limiting the claimed invention in any way.
Illustrative Embodiment
Test Methods
The following test methods were used for the measurement of the aviation
fuels.
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Motor Octane Number: ASTM D2700
Tetraethyl Lead Content: ASTM D5059
Density: ASTM D4052
Distillation: ASTM D86
Vapor Pressure: ASTM D323
Freezing Point: ASTM D2386 and ASTM D5972
Sulfur: ASTM D2622
Net Heat of Combustion (NHC): ASTM D3338
Copper Corrosion: ASTM D130
Oxidation Stability - Potential Gum: ASTM D873
Oxidation Stability - Lead Precipitate: ASTM D873
Water Reaction - Volume change: ASTM D1094
Detail Hydrocarbon Analysis: ASTM 5134
Examples 1-9
The aviation fuel compositions of the invention were blended as follows.
Toluene
having 107 MON (from VP Racing Fuels Inc.) was mixed with Aniline (from Univar
NV)
while mixing.
Isooctane (from Univar NV) and Narrow Cut Alkylate having the properties shown
in Table below (from Shell Nederland Chemie BV) were poured into the mixture
in no
particular order. Then, tert-butyl acetate or isobutyl acetate (from Univar
NV) was added,
followed by isopentane (from Matheson Tri-Gas, Inc.) to complete the blend.
Table 1
Narrow Cut Alkylate Properties
IBP (ASTM D86, C) 39.1
FBP (ASTM D86, C) 115.1
T40 (ASTM D86, C) 94.1
T50 (ASTM D86, C) 98
T90 (ASTM D86, C) 105.5
Vol % iso-05 14.52
Vol % iso-C7 7.14
Vol % iso-C8 69.35
Vol % C10+ 0
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Example 1
isopentane 18%v
Narrow range alkylate 23%v
Isooctane 20%v
High MON toluene 25%v
aniline 5%v
t-butyl acetate 9%v
Property
MON 102.5
RVP (kPa) 38.61
Freeze Point (deg C) < -65
Lead Content (g/gal) < 0.01
Density (g/mL) 0.760
Net Heat of Combustion (MJ/kg) 43.4
Adjusted Net Heat of 45.0
Combustion (MJ/kg)
Water Reaction (mL) 0
T10 (deg C) 58.6
T40 (deg C) 92.7
T50 (deg C) 99.7
T90 (deg C) 109.3
FBP (deg C) 173.3
Example 2
Isopentane 17%v
narrow cut alkylate 24%v
Isooctane 20%v
Toluene 25%v
Aniline 5%v
tert-butyl acetate 9%v
Property
MON 102.5
RVP (kPa) 38.61
Freeze Point (deg C) < -66
Lead Content (g/gal) < 0.01
Density (g/mL) 0.751
Net Heat of Combustion (MJ/kg) 42.84
Adjusted Net Heat of 44.82
Combustion (MJ/kg)
T10 (deg C) 74.4
T40 (deg C) 99.2
T50 (deg C) 101.1
T90 (deg C) 110.8
FBP (deg C) 182.9
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Example 3
isopentane 18%v
Narrow range alkylate 23%v
Isooctane 20%v
High MON toluene 25%v
aniline 5%v
isobutyl acetate 9%v
Property
MON 101.1
RVP (kPa) 46.82
Freeze Point (deg C) -60
Lead Content (g/gal) < 0.01
Density (g/mL) 0.759
Net Heat of Combustion (MJ/kg) 43.43
Adjusted Net Heat of 45.32
Combustion (MJ/kg)
T10 (deg C) 65.1
T40 (deg C) 99.9
T50 (deg C) 103.2
T90 (deg C) 116.7
FBP (deg C) 177.9
Example 4
isopentane 18%v
Narrow range alkylate 41%v
High MON toluene 25%v
aniline 6%v
t-butyl acetate 10%v
Property
MON 103.2
RVP (kPa) 47.78
Freeze Point (deg C) -60
Lead Content (g/gal) < 0.01
Density (g/mL) 0.762
Net Heat of Combustion (MJ/kg) 43.35
Adjusted Net Heat of 45.22
Combustion (MJ/kg)
T10 (deg C) 61.2
T40 (deg C) 97.9
T50 (deg C) 102.1
T90 (deg C) 118.6
FBP (deg C) 179.8
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Example 5
isopentane 16%v
Narrow range alkylate 38%v
High MON toluene 30%v
aniline 6%v
t-butyl acetate 10%v
Property
MON 102.2
RVP (kPa) 46.4
Freeze Point (deg C) <-65.5
Lead Content (g/gal) < 0.01
Density (g/mL) 0.774
Net Heat of Combustion (MJ/kg) 42.53
Adjusted Net Heat of 44.19
Combustion (MJ/kg)
T10 (deg C) 65
T40 (deg C) 99.7
T50 (deg C) 102.9
T90 (deg C) 115.3
FBP (deg C) 179.4
Example 6
isopentane 18%v
Narrow range alkylate 32%v
High MON toluene 35%v
aniline 6%v
t-butyl acetate 9%v
Property
MON 101.9
RVP (kPa) 48.26
Freeze Point (deg C) -60
Lead Content (g/gal) < 0.01
Density (g/mL) 0.779
Net Heat of Combustion (MJ/kg) 42.85
Adjusted Net Heat of 44.61
Combustion (MJ/kg)
T10 (deg C) 62.4
T40 (deg C) 100.6
T50 (deg C) 103.9
T90 (deg C) 114.3
FBP (deg C) 177.9
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Example 7
isopentane 18%v
Narrow range alkylate 38%v
High MON toluene 30%v
aniline 5%v
t-butyl acetate 9%v
Property
MON 101.3
RVP (kPa) 48.54
Freeze Point (deg C) < -80
Lead Content (g/gal) < 0.01
Density (g/mL) 0.771
Net Heat of Combustion (MJ/kg) 42.8
Adjusted Net Heat of 44.2
Combustion (MJ/kg)
Water Reaction (mL) 1
T10 (deg C) 62.8
T40 (deg C) 100.4
T50 (deg C) 103.8
T90 (deg C) 114.2
FBP (deg C) 179.6
Example 8
isopentane 18%v
Narrow range alkylate 24%v
Isooctane 20%v
High MON toluene 25%v
aniline 4%v
t-butyl acetate 9%v
Property
MON 101.2
RVP (kPa) 45.23
Freeze Point (deg C) < -79
Lead Content (g/gal) < 0.01
Density (g/mL) 0.759
Net Heat of Combustion (MJ/kg) 42.87
Adjusted Net Heat of 44.55
Combustion (MJ/kg)
Water Reaction (mL) 0
T10 (deg C) 65
T40 (deg C) 98.7
T50 (deg C) 101.6
T90 (deg C) 110.7
FBP (deg C) 161.2
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Example 9
isopentane 18%v
Narrow range alkylate 20%v
Isooctane 20%v
High MON toluene 30%v
aniline 3%v
t-butyl acetate 9%v
Property
MON 100.9
RVP (kPa) 38.2
Freeze Point (deg C) < -70
Lead Content (g/gal) < 0.01
Density (g/mL) 0.774
Net Heat of Combustion (MJ/kg) 42.38
Adjusted Net Heat of 43.99
Combustion (MJ/kg)
Water Reaction (mL) 0
T10 (deg C) 71.2
T40 (deg C) 100
T50 (deg C) 102
T90 (deg C) 109.6
FBP (deg C) 158.8
Properties of an Alkylate Blend
Properties of an Alkyalte Blend containing 1/2 narrow cut alkylate (having
properties as shown above) and 1/2 Isooctane is shown in Table 2 below.
Table 2
Alkylate Blend Properties
IBP (ASTM D86, C) 54.0
FBP (ASTM D86, C) 117.5
T40 (ASTM D86, C) 97.5
T50 (ASTM D86, C) 99.0
T90 (ASTM D86, C) 102.5
Vol % iso-05 5.17
Vol % iso-C7 3.60
Vol % iso-C8 86.83
Vol % C10+ 0.1
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Combustion Pro_perties
In addition to the physical characteristics, an aviation gasoline should
perform well
in a spark ignition reciprocating aviation engine. A comparison to the current
leaded
aviation gasoline found commercially is the simplest way to assess the
combustion
properties of a new aviation gasoline.
Table 3 below provides the measured operating parameters on a Lycomin TgM T I
0 -
540 J213D engine for avgas Example 1 and a commercially purchased 100 LL avgas
(FBO 1 OOLL).
Table 3
Brake
Fuel Turbine Inlet
Brake Specific Fuel
Altitude
Consumption CHTa,Cyl Temperature Horsepower Consumption
Fuel (ft) RPM (lbs/hr) 1 ( F) (F) (Observed)
(1b./hp.-hr)
FBO lOOLL 3000 2575.09 212.35 472 1533 330.45
0.642
Example 1 3000 2575.01 202.7 450 1613 332.65
0.609
FBO 100LL 6000 2199.98 128.42 457 1615 256.54
0.495
Example I 6000 2199.98 143.85 450 1603 263.15
0.547
FBO 1 OOLL 8000 2575.16 221.27 464 1544 350.76
0.632
Example 1 8000 2574.93 219.22 454 1626 365.73
0.599
FBO lOOLL 12000 2400.01 184.19 461 1520 297.77
0.618
Example 1 12000 2399.98 185.34 441 1577 301.05
0.616
aCHT = cylinder head temperature. Although testing was conducted on a six
cylinder engine, the variation
between I OOLL and Example 1 results were similar over all six cylinders, so
only cylinder l values are used
for representation. Reference Figures 1, 3, 5, 7, 9, 11, 13, 15 for more
complete data.
As can be seen from Table 3 that the avgas of the invention provides similar
engine
operating characteristics compared to the leaded reference fuel. The data
provided in Table
3 was generated using a LycominTTIO-540 J2BD six cylinder reciprocating spark
ignition
aviation piston engine mounted on an engine test dynamometer. Of particular
note are the
fuel consumption values. Given the higher density of the fuel, it would be
expected that
the test fuel would require significantly higher fuel consumption in order to
provide the
same power to the engine. It is clear from Table 3 that the observed fuel
consumption
values are very similar across all test conditions, further supporting the use
of an adjusted
heat of combustion (HOC*) to compensate for fuel density effects in the
evaluation of a
fuel's impact on the range of an aircraft.
In order to assure transparency with the existing leaded gasoline, the ability
of an
aviation engine to operate within its certified operating parameters when
using an unleaded
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aviation fuel, such as cylinder head temperatures and turbine inlet
temperatures over a
range of air/fuel mixtures, was assessed using engine certification test
normally submitted
to FAA for a new engine. The test was run for unleaded aviation fuel Example 1
which
results are shown in Figures 1 to 8 and for a commercial 100 LL fuel shown in
Figures 9 to
16. The detonation data were obtained using the procedure specified in ASTM
D6424. As
can be seen in Figures 1, 3, 5 and 7 for the Example 1 test fuel and Figures
9, 11, 13 and 15
for the FBO sourced 1 OOLL (101MON) reference fuel, the Lycoming IO 540 J2BD
engine
was able to operate over its entire certified operating range without issue
using aviation
fuel of Example lwith no noticeable change in operating characteristics from
operation
with the lOOLL reference fuel.
In order to fully evaluate the ability of an engine to operate correctly using
a given
fuel over its entire operating range, the resistance of the fuel to detonate
must be included.
Therefore, the fuel was evaluated for detonation against an FBO procured 1
OOLL reference
fuel (101 MON) at four conditions, 2575RPM at constant manifold pressure
(Example 1
Fig. 2, lOOLL reference Fig 10), 2400 RPM at constant manifold pressure
(Example 1 Fig.
4, 1 OOLL reference Fig. 12), 2200 RPM at constant manifold pressure (Example
1 Fig. 6,
1 OOLL reference Fig 14) and 2757 RPM at constant power (Example 1 Fig. 8, 1
OOLL
reference Fig 16). These conditions provide the most detonation sensitive
operating
regions for this engine, and cover both lean and rich operation.
As can be seen from the detonation plots referenced-above, the unleaded
aviation
fuel or the invention performs comparably to the current lOOLL leaded aviation
fuel. Of
particular importance is that the unleaded fuel experiences detonation at
lower fuel flow
than the comparable leaded fuel. Additionally, when detonation does occur,
this observed
intensity of this effect is typically smaller than that found for the leaded
reference fuel.
Materials Compatibility
The Material (nitrile rubber in the wing bladder tanks of a Piper Saratoga:
Part
number 461-710) was soaked in 500 ml of aviation fuel in a screw-on-top glass
jar and left
at room temperature for 28 days.
The Material was tested with two fuels: Example 1 and an FBO procured 1 OOLL
aviation gasoline.
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After the soaking period, the material was pulled out of the fuels, air dried
and
visually examined. Material showed no delaminating, swelling, shrinking, or
any
deterioration upon visual inspection.
It was, therefore, given a "Pass" grade.
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Comparative Examples A-K
Comparative Examples A and B
A high octane unleaded aviation gasoline that use large amounts of oxygenated
materials as described in US Patent Application Publication 2008/0244963 as
Blend X4
and Blend X7 is provided. The reformate contained 14vol% benzene, 39vo1%
toluene and
47vo1% xylene.
Comparative A Vol % Comparative B Vol %
Blend X4 Blend X7
Isopentane 12.25 Isopentane 12.25
Aviation alkylate 43.5 Aviation alkylate 43.5
Reformate 14 Reformate 14
Diethyl carbonate 15 Diethyl carbonate 8
m-toluidine 3 m-toluidine 2
MIBK 12.46 MIBK 10
phenatole 10
Property Blend X4 Blend X7
MON 100.4 99.3
RVP (kPa) 35.6 40.3
Freeze Point (deg C) -51.0 -70.0
Lead Content (g/gal) < 0.01 < 0.01
Density (g/mL) 0.778 0.781
Net Heat of Combustion 38.017 39.164
(MJ/kg)
Adjusted Net Heat of 38.47 39.98
Combustion (MJ/kg)
Oxygen Content (%m) 8.09 6.16
T10 (deg C) 73.5 73
T40 (deg C) 102.5 104
T50 (deg C) 106 108
T90 (deg C) 125.5 152.5
FBP (deg C) 198 183
The difficulty in meeting many of the ASTM D-910 specifications is clear given
these results. Such an approach to developing a high octane unleaded aviation
gasoline
generally results in unacceptable drops in the heat of combustion value ( >
10% below
ASTM D910 specification) and final boiling point. Even after adjusting for the
higher
density of these fuels, the adjusted heat of combustion remains too low.
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Comparative Examples C and D
A high octane unleaded aviation gasoline that use large amounts of mesitylene
as
described as Swift 702 in US Patent No. 8313540 is provided as Comparative
Example C.
A high octane unleaded gasoline as described in Example 4 of US Patent
Application
Publication Nos. US20080134571 and U520120080000 are provided as Comparative
Example D.
Comparative Vol % Comparative Vol%
Example C Example D
Isopentane 17 Isopentane 3.5
mesitylene 83 alkylate 45.5
Toluene 23
Xylenes 21
aniline 7
Property Comparative Example C
Comparative Example D
MON 105 104
RVP (kPa) 35.16 17.79
Freeze Point (deg C) -20.5 -41.5
Lead Content (g/gal) < 0.01 <0.01
Density (g/mL) 0.830 0.794
Net Heat of Combustion 41.27 42.20
(MJ/kg)
Adjusted Net Heat of 42.87 43.86
Combustion (MJ/kg)
T10 (deg C) 74.2 100.4
T40 (deg C) 161.3 108.3
T50 (deg C) 161.3 110.4
T90 (deg C) 161.3 141.6
FBP (deg C) 166.1 180.2
As can be seen from the properties, the Freeze Point is too high for both
Comparative Examples C & D.
Comparative Examples E-K
Other comparative examples where the components were varied are provided
below. As can been seem from the above and below examples, the variation in
composition
resulted in at least one of MON being too low, RVP being too high or low,
Freeze Point
being too high, or Heat of Combustion being too low.
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Comparative Vol % Comparative Vol %
Example E Example F
Isopentane 10 Isopentane 15
Aviation alkylate 60 isooctane 60
m-xylene 30 toluene 25
Property Comparative Example E
Comparative Example F
MON 93.6 95.4
RVP (kPa) 40 36.2
Freeze Point (deg C) < -80 < -80
Lead Content (g/gal) < 0.01 < 0.01
Density (g/mL) 0.738 0.730
Net Heat of Combustion 43.11 43.27
(MJ/kg)
Adjusted Net Heat of 44.70 44.83
Combustion (MJ/kg)
T10 (deg C) 68.4 76.4
T40 (deg C) 106.8 98.7
T50 (deg C) 112 99.7
T90 (deg C) 134.5 101.3
FBP (deg C) 137.1 115.7
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Comparative Vol % Comparative Vol %
Example G Example H
Isopentane 15 Isopentane 10
Isooctane 75 Aviation alkylate 69
Toluene 10 toluene 15
m-toluidine 6
Property Comparative Example G Comparative Example
H
MON 96 100.8
RVP (kPa) 36.9 44.8
Freeze Point (deg C) < -80 -28.5
Density (g/mL) 0.703 0.729
Lead Content (g/gal) < 0.01 < 0.01
Net Heat of Combustion 44.01 43.53
(MJ/kg)
Adjusted Net Heat of 45.49 45.33
Combustion (MJ/kg)
T10 (deg C) 75.3 65
T40 (deg C) 97.1 96.3
T50 (deg C) 98.4 100.6
T90 (deg C) 99.1 112.9
FBP (deg C) 111.3 197.4
Comparative Vol % Comparative Vol %
Example I Example J
Isopentane 15 Isopentane 15
Narrow cut alkylate 24 Narrow cut alkylate 24
Isooctane 25 isooctane 25
Toluene 25 toluene 25
Aniline 6 Aniline 6
Isobutyl acetate 5 Tert-butyl acetate 5
Property Comparative Example I Comparative Example J
MON 100.8 100.7
RVP (kPa) 40.61 34.06
Freeze Point (deg C) -46 -29.5
Lead Content (g/gal) < 0.01 < 0.01
Density (g/mL) 0.757 0.758
Net Heat of Combustion 42.85 42.81
(MJ/kg)
Adjusted Net Heat of 44.51 44.46
Combustion (MJ/kg)
T10 (deg C) 69 78
T40 (deg C) 99.5 100.5
T50 (deg C) 102.5 101.5
T90 (deg C) 115 113.5
FBP (deg C) 184 180
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Comparative Vol %
Example K
Isopentane 15
Narrow cut alkylate 24
Isooctane 25
Toluene 25
Aniline 6
2-ethyl hexanol 5
Property Comparative Example K
MON 98.8
RVP (kPa) 40. 26
Freeze Point (deg C) -27
Lead Content (g/gal) < 0.01
Density (g/mL) 0.756
Net Heat of Combustion 42.87
(MJ/kg)
Adjusted Net Heat of 44.53
Combustion (MJ/kg)
T10 (deg C) 68
T40 (deg C) 100
T50 (deg C) 102.5
T90 (deg C) 133.5
FBP (deg C) 182.5
26
